1. Field of the Invention
This invention relates to defined probiotics for the control of Salmonella colonization in domestic animals including fowl, and particularly chickens.
Despite the efforts of researchers and public health agencies, the incidence of human salmonellosis has increased over the past 20 years. The number of actual reported cases of human Salmonella infection exceeds 40,000 per year. However, the Communicable Disease Center estimates that the true incidence of human Salmonella infections in the U.S. each year may be as high as 2 to 4 million. Animal food products, including poultry, remain the principal source of human infection.
2. Description of the Prior Art
Considering the widespread presence of Salmonella in the environment, it is unlikely that poultry can be completely protected from Salmonella exposure. Therefore, researchers have continued to investigate means of increasing resistance to colonization in poultry exposed to Salmonella. Studies have focused on the evaluation of vaccines, establishment of protection normal intestinal flora, and the identification of feed additives that will inhibit Salmonella growth and colonization. The role of host immunity against Salmonella colonization is unclear, and it also remains uncertain if stimulation of immune responses will effectively enhance colonization resistance. Experimental vaccines have not proven to be consistently effective.
It is well documented that normal intestinal microflora increase resistance against Salmonella colonization. Oral inoculation of young chicks with anaerobic bacterial cultures of microflora, also known as probiotics (defined as bacterial cultures which have a beneficial effect on the animal to which they are administered), prepared from the cecal contents or fecal droppings of mature chickens has proven to effectively reduce Salmonella colonization [Shoeyenbos et al., Avian Dis., 23:904-913, (1979), Schneitz et al., Acta Pathol. Microbiol. Scand. Sect. B., 89:109-116, (1981), and Stavric et al., J. Food Prot., 48:778-782, (1985)]. Conversely, poultry rearing practices that prevent chicks from becoming colonized by these cecal anaerobes make the chicks more susceptible to Salmonella colonization [Pivnick et al., J. Food Prot., 44:909-916, (1981)]. These probiotics may decrease Salmonella colonization by rapidly colonizing the intestinal tract of the young chicks (Pivnick et al., ibid), by competing for attachment sites on the intestinal wall (Snoeyenbos et al., ibid), or by producing bacteriostatic or bactericidal short-chained volatile fatty acids [Barnes et al., J. Hyg. Camb., 82:263-183, ( 1979) and Am. J. Clin. Nutr., 33:2426-1433, (1980), Corrier et al., Avian Dis., 34:668-676, (1990) and Avian Dis., 34:617-625, (1990), and Hinton et al., Avian Dis., 34:626-633, (1990)] that inhibit the growth of enteropathogens.
However, only cultures of normal microflora that contain a mixed population of several hundred different micro-organisms have proven to effectively inhibit Salmonella growth. Establishment of normal intestinal flora in day-old chicks using mixed cultures of micro-organisms has been widely used to control Salmonella colonization in several European countries. Yet, because of the undefined number and types of micro-organisms present in mixed cultures, the system has not been widely accepted in the United States. One drawback to the widespread use of the this method has been the fact that the composition of the product cannot be standardized, and thus the product cannot be stored or produced on a large scale without changes in composition and effectiveness. Also, because the starting material is always the intestinal content of an adult fowl, the product may contain pathogenic viruses, bacteria, or parasites, which may be dangerous to the health of the chicks. Further still, the U.S. Food & Drug Administration has recently required that all undefined cultures must be approved.
Lactose and other milk sugar products added to the feed or water of chicks have recently been reported to enhance resistance against Salmonella colonization [Oyofo et al., Avian Dis., 33:531-534, (1989) and Poultry Sci., 68:1357-1360, (1989), Corrier et al., ibid, and Hinton et al., ibid.]. Dietary lactose increases the acidity of the cecal contents and influences the growth and fermentation products of normal intestinal microflora. Lactose supplemented diets may also enhance Salmonella colonization resistance by increasing the bacteriostatic action of short chain volatile fatty acids such as acetic, propionic, and butyric acids, produced by some normal intestinal bacterial [Corrier et al., ibid, Hinton et al., ibid].
Resistance to Salmonella colonization in chicks has also further been increased when the chicks are provided the combination of dietary lactose and cultures of cecal anaerobes grown in a lactose containing broth [Corrier et al. and Hinton et al., ibid].